Time-of-flight mass spectrometer

A time-of-flight mass spectrometer capable of cutting out a major portion of carrier gas-derived ions ahead of the ion reservoir. The ion source is of the electron impact type and has source magnets for deflecting some of the produced ions away from the center axis of the ion reservoir. Electrostatic lenses for promoting the deflection of the ions caused by the source magnets and a differentially pumped slit for cutting off the deflected ions are mounted downstream of the ion source.